Selective Production of Rydberg-Stark States of Positronium

Rydberg positronium (Ps) atoms have been prepared in selected Stark states via two-step (1s→2p→nd/ns) optical excitation. Two methods have been used to achieve Stark-state selection: a field ionization filter that transmits the outermost states with positive Stark shifts, and state-selected photoexcitation in a strong electric field. The former is demonstrated for n=17 and 18 while the latter is performed for n=11 in a homogeneous electric field of 1.9  kV/cm. The observed spectral intensities and their dependence on the polarization of the laser radiation are in agreement with calculations that include the perturbations of the intermediate n=2 manifold. Our results pave the way for the generation of Rydberg Ps atoms with large electric dipole moments that are required for the realization of schemes to control their motion using inhomogeneous electric fields, an essential feature of some proposed Ps free-fall measurements requiring focused beams of long-lived atoms

Resonant shifts of positronium energy levels in MgO powder

We report measurements of shifts in the frequencies of 13S1→23PJ and 23PJ→n3D/n3S transitions optically driven in positronium atoms while they are inside the open volumes of MgO smoke powder. The observed intervals are larger than the corresponding vacuum excitations, but, surprisingly, the transitions to Rydberg states are less strongly affected, and the energy shifts exhibit no dependence on the principal quantum number n of the final state. We attribute these shifts to resonant interactions between Ps atoms and MgO surfaces, mediated via spectrally overlapping MgO ultra violet (UV) photo-luminescent absorption bands. Since many insulating materials suitable for Ps confinement exhibit similar broadband UV absorption characteristics, the observed phenomena have implications for optical diagnostics and laser cooling schemes of relevance to studies of high-density Ps ensembles in insulating cavities, including the production of a Ps Bose-Einstein condensate

Electrostatically Guided Rydberg Positronium

We report experiments in which positronium (Ps) atoms were guided using inhomogeneous electric fields. Ps atoms in Rydberg-Stark states with principal quantum number n=10 and electric dipole moments up to 610 D were prepared via two-color two-photon optical excitation in the presence of a 670  V cm−1 electric field. The Ps atoms were created at the entrance of a 0.4 m long electrostatic quadrupole guide, and were detected at the end of the guide via annihilation gamma radiation. When the lasers were tuned to excite low-field-seeking Stark states, a fivefold increase in the number of atoms reaching the end of the guide was observed, whereas no signal was detected when high-field-seeking states were produced. The data are consistent with the calculated geometrical guide acceptance

Positronium decay from n=2 states in electric and magnetic fields

We report measurements and the results of calculations demonstrating that the annihilation dynamics of positronium (Ps) atoms can be controlled by Stark and Zeeman mixing of optically excited states. In the experiments a trap-based pulsed positron beam was employed to generate a dilute Ps gas with a density of ∼107 cm−3 using a porous silica target. These atoms were excited via 13S1→23PJ transitions in parallel electric and magnetic fields using a nanosecond pulsed dye laser, and Ps annihilation was measured using single-shot lifetime spectroscopy. The composition of the excited n=2 sublevels was controlled by varying the polarization of the excitation laser radiation and the strength of the electric and magnetic fields in the excitation region. The overall decay rates of the excited states can vary by a large amount, owing to the enormous differences between the annihilation and florescence lifetimes of the accessible field-free states. The energy-level structure, spectral intensities, and florescence and annihilation lifetimes in the presence of the fields were determined from the eigenvalues and eigenvectors of the complete n=2 Hamiltonian matrix in an |nSℓJMJ⟩ basis. Using these data as the input to a Monte Carlo model yielded calculated values which could be compared with experimentally measured quantities; qualitative agreement with the measurements was found. Varying the electric field in the presence of a weak parallel magnetic field provides control over the amount of level mixing that occurs, making it possible to increase or decrease the Ps lifetime. Field-controlled Ps decay can be used as an ionization-free detection method. Conversely, increasing the excited-state lifetime can potentially be exploited to optimize multistep excitation processes using mixed intermediate states. This will be useful either in minimizing losses through intermediate-state decay during excitation or by making it possible to separate excitation laser pulses in time. In addition, the adiabatic extraction of appropriate eigenstates from the electric field in which they are excited can, in principle, be used to prepare pure 23S1 atoms. The availability of atoms in these states produced via single-photon excitation will facilitate high-resolution microwave spectroscopy of the Ps n=2 fine structure

Measurement of Rydberg positronium fluorescence lifetimes

We report measurements of the fluorescence lifetimes of positronium (Ps) atoms with principal quantum numbers n=10–19. Ps atoms in Rydberg-Stark states were produced via a two-color two-step 1S3→2P3→nS3/nD3 excitation scheme and subsequently detected after traveling 1.2 m. The measured time-of-flight distributions were used to determine the mean lifetimes of the Rydberg levels, yielding values ranging from 3μs to 26μs. Our data are in accord with the expected radiative lifetimes of Rydberg-Stark states of Ps

Fire effects on aquatic ecosystems: an assessment of the current state of science

Fire is a prevalent feature of many landscapes and has numerous and complex effects on geological, hydrological, ecological, and economic systems. In some regions, the frequency and intensity of wildfire have increased in recent years and are projected to escalate with predicted climatic and landuse changes. In addition, prescribed burns continue to be used in many parts of the world to clear vegetation for development projects, encourage desired vegetation, and reduce fuel loads. Given the prevalence of fire on the landscape, authors of papers in this special series examine the complexities of fire as a disturbance shaping freshwater ecosystems and highlight the state of the science. These papers cover key aspects of fire effects that range from vegetation loss and recovery in watersheds to effects on hydrology and water quality with consequences for communities (from algae to fish), food webs, and ecosystem processes (e.g., organic matter subsidies, nutrient cycling) across a range of scales. The results presented in this special series of articles expand our knowledge of fire effects in different biomes, water bodies, and geographic regions, encompassing aquatic population, community, and ecosystem responses. In this overview, we summarize each paper and emphasize its contributions to knowledge on fire ecology and freshwater ecosystems. This overview concludes with a list of 7 research foci that are needed to further our knowledge of fire effects on aquatic ecosystems, including research on: 1) additional biomes and geographic regions; 2) additional habitats, including wetlands and lacustrine ecosystems; 3) different fire severities, sizes, and spatial configurations; and 4) additional response variables (e.g., ecosystem processes) 5) over long (>5 y) time scales 6) with more rigorous study designs and data analyses, and 7) consideration of the effects of fire management practices and policies on aquatic ecosystems

Cognitive architectures as Lakatosian research programmes: two case studies

Cognitive architectures - task-general theories of the structure and function of the complete cognitive system - are sometimes argued to be more akin to frameworks or belief systems than scientific theories. The argument stems from the apparent non-falsifiability of existing cognitive architectures. Newell was aware of this criticism and argued that architectures should be viewed not as theories subject to Popperian falsification, but rather as Lakatosian research programs based on cumulative growth. Newell's argument is undermined because he failed to demonstrate that the development of Soar, his own candidate architecture, adhered to Lakatosian principles. This paper presents detailed case studies of the development of two cognitive architectures, Soar and ACT-R, from a Lakatosian perspective. It is demonstrated that both are broadly Lakatosian, but that in both cases there have been theoretical progressions that, according to Lakatosian criteria, are pseudo-scientific. Thus, Newell's defense of Soar as a scientific rather than pseudo-scientific theory is not supported in practice. The ACT series of architectures has fewer pseudo-scientific progressions than Soar, but it too is vulnerable to accusations of pseudo-science. From this analysis, it is argued that successive versions of theories of the human cognitive architecture must explicitly address five questions to maintain scientific credibility

Technical performance and diagnostic utility of the new Elecsys (R) neuron-specific enolase enzyme immunoassay

This international multicenter study was designed to evaluate the technical performance of the new double-monoclonal, single-step Elecsys neuron-specific enolase (NSE) enzyme immunoassay (EIA) and to assess its utility as a sensitive and specific test for the diagnosis of small-cell lung cancer (SCLC). Intra and interassay coefficients of variation, determined in five control or serum specimens in six laboratories, ranged from 0.7 to 5.3 (interlaboratory median: 1.3%) and from 1.3 to 8.5 (interlaboratory median: 3.4%), respectively. Laboratory-to-laboratory comparability was excellent with respect to recovery and interassay coefficients of variation. The test was linear between 0.0 and 320 ng/ml (highest measured concentration). There was a significant correlation between NSE concentrations measured using the Elecsys NSE and the established Cobas Core NSE EIA II in all subjects (n=723) and in patients with lung cancer (n=333). However, NSE concentrations were systematically lower (approximately 9%) with the Elecsys NSE than with the comparison test. Based on a specificity of 95% in comparison with the group suffering from benign lung diseases (n=183), the cutoff value for the discrimination between malignant and benign conditions was set at 21.6 ng/ml. NSE was raised in 73.4% of SCLC patients (n=188) and was significantly higher (p<0.01) in extensive (87.8%) as opposed to limited disease (56.7%). NSE was also elevated in 16.0% of the cases with non-small cell lung cancer (NSCLC, n=374). It is concluded that the Elecsys NSE EIA is a reliable and accurate diagnostic procedure for the measurement of NSE in serum samples. The special merits of this new assay are the wide measuring range (according to manufacturers declaration up to 370 ng/ml) and a short incubation time of 18 min

Improving health and well-being through community health champions: a thematic evaluation of a programme in Yorkshire and Humber.

AIMS: The contribution that lay people can make to the public health agenda is being increasingly recognised in research and policy literature. This paper examines the role of lay workers (referred to as 'community health champions') involved in community projects delivered by Altogether Better across Yorkshire and Humber. The aim of the paper is to describe key features of the community health champion approach and to examine the evidence that this type of intervention can have an impact on health. METHODS: A qualitative approach was taken to the evaluation, with two strands to gathering evidence: interviews conducted with different stakeholder groups including project leads, key partners from community and statutory sectors and community workers, plus two participatory workshops to gather the views of community health champions. Seven projects (from a possible 12) were identified to be involved in the evaluation. Those projects that allowed the evaluation team to explore fully the champion role (training, infrastructure, etc.) and how that works in practice as a mechanism for empowerment were selected. In total, 29 semi-structured interviews were conducted with project staff and partners, and 30 champions, varying in terms of age, gender, ethnicity and disability, took part in the workshops. RESULTS: Becoming a community health champion has health benefits such as increased self-esteem and confidence and improved well-being. For some champions, this was the start of a journey to other opportunities such as education or paid employment. There were many examples of the influence of champions extending to the wider community of family, friends and neighbours, including helping to support people to take part in community life. Champions recognised the value of connecting people through social networks, group activities, and linking people into services and the impact that that had on health and well-being. Project staff and partners also recognised that champions were promoting social cohesiveness and helping to integrate people into their community. CONCLUSIONS: The recent public health White Paper suggested that the Altogether Better programme is improving individual and community health as well as increasing social capital, voluntary activity and wider civic participation. This evaluation supports this statement and suggests that the community health champion role can be a catalyst for change for both individuals and communities

Patients' perceptions of the potential of breathing training for asthma: a qualitative study.

Poor symptom control is common in asthma. Breathing training exercises may be an effective adjunct to medication; it is therefore important to understand facilitators and barriers to uptake of breathing training exercises